1. Field of the Invention
The present invention is generally related to a trim tab position monitor and, more particularly, to a monitoring circuit which determines the position of a trim tab of a marine vessel by determining the number of changes in magnitude of an electrical characteristic of a motor which is attached to the trim tab.
2. Description of the Prior Art
Many different ways are known for measuring the angular position of a trim tab relative to a transom of a marine vessel.
U.S. Pat. No. 4,420,741, which issued to West on Dec. 13, 1983, describes a trim tab position monitor and display device. An electric position monitor and read out device for trim tabs on boats is described in which the monitor and read out device are connected to the trim tab controls. The device is electronic and position display is based on the time required for trim tab movement. Signals from the trim tab controls produce signals from timers which in turn are directed to enabling circuits. If the enabling circuits pass the timer signals, they are counted in counter circuits and hence directed to a decoder and finally to the display panel. The display panel is arranged to show the precise angular position of the trim tabs to the boat operator.
U.S. Pat. No. 4,644,893, which issued to Zepp on Feb. 24, 1987, describes a position indicating apparatus for use in a boat leveling system. The boat leveling system has a pair of trim tabs which are pivotal between a horizontal position and a downward inclined position. Each trim tab is actuatable between the horizontal and inclined positions by a separate fluid motor which includes a cylinder, a piston slidably disposed in the cylinder and a rod connected to the piston. The position of each trim tab is indicated by apparatus which includes a linear potentiometer attached to the rod of the associated fluid motor, the potentiometer having a flexible plastic envelope and a pair of normally spaced apart conductive strips sealed in the envelope, a ball and spring carried by the cylinder for contacting the envelope and forcing the strips into electrical contact with each other, and a resistance measuring device connected in circuit with the potentiometer and to provide a readout in degrees of the downward angle from the horizontal of the trim tab.
U.S. Pat. No. 4,854,259, which issued to Cluett on Aug. 8, 1989, describes an improved trim tab control system for power boats. The trim tab control for boats has for each trim tab a yoke movably secured to a frame, a mechanical link between the yoke and the trim tab such that yoke and trim tab move in unison, a lever pivotably mounted with respect to the yoke and having first and second engagement surfaces, and a pair of switches on the yoke positioned for selective engagement with the lever surfaces to actuate a hydraulic device for moving the trim tab in opposite directions. Tab adjustment is carried out by continuing movement of the lever with respect to the yoke, which the yoke moves in response to such adjustment. A scale is secured adjacent to the lever such that the lever position provides visual indication of the trim tab position.
U.S. Pat. No. 5,385,110, which issued to Bennett et al on Jan. 31, 1995, describes a boat trim control and monitor system. A boat trim control system that includes a boat having a hull and means such as trim tabs mounted on the hull for trimming attitude of the boat as the hull is propelled through the water. The system includes facility for selectively adjusting the trim tabs to maintain a desired boat attitude under varying load and sea conditions. A sensor is mounted on the boat hull to provide an electrical sensor signal as a function of boat attitude, and is connected to electronic control circuitry responsive to the sensor signal for determining attitude of the boat hull. This electronic control circuitry further includes facility for operator setting of a desired boat attitude. The electronic control circuitry is coupled to an operator display for indicating departure of actual boat attitude indicated by the sensor from the boat attitude desired by the operator, and/or to automatic control circuitry for automatically varying trim tab orientation with respect to the boat hull so as to maintain the boat attitude desired by the operator.
U.S. Pat. No. 5,474,013, which issued to Wittmaier on Dec. 12, 1995, describes a trim tab auto-retract and multiple switching device. Electromechanical control circuit for causing trim tabs attached to the stern of a hull of a motorized marine vessel, and used to trim the attitude of the vessel, to be automatically fully retracted by activating means independently of the boat ignition switch to cause a capacitor in the circuit to discharge is described. The means can include at least one switch connected between the capacitor and the electrical power source to which the control circuit can be connected such that the means are activated when the switch is opened. The switch can be positioned at multiple locations throughout the boat or, alternatively, controls to cause the switch to open can be mounted to the boat at multiple locations throughout the craft, including at the main control panel. The means can also be in communication with the boat engine gear shift controls such that the means are activated when the vessel engine is shifted into reverse gear. The control circuit further includes means for preventing damage to the circuit components if the circuit is improperly connected to the electrical power source.
U.S. Pat. No. 6,273,771, which issued to Buckley et al on Aug. 14, 2001, discloses a control system for a marine vessel. A control system incorporates a marine propulsion system that can be attached to a marine vessel and connected in signal communication with a serial communication bus and a controller. A plurality of input devices and output devices are also connected in signal communication with the communication bus and a bus access manager, such as a CAN Kingdom network, is connected in signal communication with the controller to regulate the incorporation of additional devices to the plurality of devices in signal communication with the bus whereby the controller is connected in signal communication with each of the plurality of devices on the communication bus. The input and output devices can each transmit messages to the serial communication for receipt by other devices.
U.S. Pat. No. 4,742,794, which issued to Hagstrom on May 10, 1988, describes a trim tab indicator system. The indicator system comprises a pair of trim members hinged to the stern of a boat, one on each side of the center line of the boat and a hydraulic cylinder attached to each trim member having a first head at one end and a second head at the other end. The cylinder includes a piston and a tubular shaft connected to the piston and extending through the first end of the cylinder. A bracket is connected to the first head and has a surface complementary to the transom of the boat and is mounted on the transom. A tubular coil is fixed on the first head and extends axially within the cylinder, and a floating rod of magnetically permeable material is provided in the tubular shaft with a lower end engaging the base of the tubular opening of the shaft with its upper end extending into the coil such that movement of the trim tab changes the inductive relationship between the rod and the coil to provide a signal representing the position of the tab.
U.S. Pat. No. 6,280,269, which issued to Gaynor on Aug. 28, 2001, discloses an operator display panel control by throttle mechanism switch manipulation. A throttle control mechanism is provided with a plurality of buttons and a control unit that interprets the state of the various buttons and switches in different ways, depending on the state of a first operating parameter. The first operating parameter can be the gear selector position or the status of a manual selector switch or push button. Based on the state of the first operating parameter, at least one switch is interpreted to represent a first command based on a first state of the first operating parameter and a second command based on the second state of the first operating parameter. This allows dual functionality for the buttons and switches which reduces the required number of switches and also allows the important control switches to be placed easily within reach of the operator of a marine vessel.
The patents described above are hereby expressly incorporated by reference in the description of the present invention.
Known trim tab position monitoring devices typically incorporate sensors, such as Hall effect devices or potentiometers, which are physically attached to the trim tabs or the pressure cylinders used to move the trim tabs. It is also known that motors can be used to move actuating rods that, in turn, are attached to the trim tabs to move the trim tabs in response to movement of the motor. When position sensing devices are located at or near the trim tabs themselves, those devices are subjected to the corrosive and potential damaging effects of submersion in water. These effects can be particularly deleterious when a marine vessel is operated in salt water. It would therefore be significantly advantageous if a means could be provided for determining the position of the trim tabs relative to the transom of a boat without having to physically measure the angular position of the trim tab at the location proximate the trim tab. It would also be significantly beneficial if the trim tab position could be determined without the requirement of additional expensive measuring equipment or sensors.
The trim tab monitor made in accordance with the preferred embodiment of the present invention comprises a sensing circuit connected in signal communication with a stator of a motor. The motor has a rotor and a stator. The rotor is operatively connected to the trim tab for moving the trim tab relative to the marine vessel. The sensing circuit is configured to provide a first output signal which is representative of a preselected electrical characteristic of the motor. In a particularly preferred embodiment of the present invention, the first output signal represents an electrical characteristic relating the voltage potential across the stator of the motor which exhibits fluctuations as a result of the movement of rotor poles past the various portions of the stator winding. These fluctuations are caused by the reverse electromotive force (emf) experienced by the stator winding. The present invention further comprises a direction determining circuit that is connected in electrical communication with the sensing circuit. The direction determining circuit is configured to provide a second signal which is representative of the rotational direction (i.e. clockwise or counterclockwise) of the rotor relative to the stator of the motor. The present invention further comprises a counter connected in electrical communication with a sensing circuit and configured to provide a third output signal which is representative of a preselected number of magnitude changes of the first output signal. This counter is typically a xe2x80x9cdivide byxe2x80x9d counter which provides an output signal pulse at a rate which is some reduced factor of the rate of the pulses received by the counter. For example, a counter may be configured to provide a single output pulse for every 128 input pulses, or any other predetermined number of input pulses selected as a function of the type of application in which the present invention is used. The present invention further comprises a signal output device connected in electrical communication with the counter for providing a fourth output signal which is representative of the position of the trim tab relative to the motor.
It should be understood that the present invention actually provides an output signal that represents the physical condition of the point at which the trim tab is connected to a moveable actuator that is driven by the rotor of the motor. This output signal may represent a magnitude that has a nonlinear relationship to the physical angle of the trim tab relative to the transom of a marine vessel. As will be described in greater detail below, an output device or output monitor can be provided with a conversion table that easily converts the output received from the present invention to an angle representing the resulting angle between the trim tab and the transom of the boat or, alternatively, an angle between the trim tab and a horizontal plane.
The electrical characteristic of the motor can be a voltage potential across the stator of the motor which exhibits magnitude fluctuations that are caused by the rotation of the rotor relative to the stator. As described above, these fluctuations can be caused by the reverse electromotive force experienced by the stator when poles of the rotor pass certain portions of the stator. The sensing circuit can comprise a differential amplifier circuit connected in signal communication with the stator of the motor and can also comprise a low pass filter for separating an AC component of the electrical characteristic from a DC component of the electrical characteristic. The sensing circuit can also comprise a zero crossing detector which is configured to provide a fifth output signal. The zero crossing detector is connected in signal communication with the counter.
In a particularly preferred embodiment of the present invention, the signal output device is connected in signal communication with the counter and in signal communication with a boat position annunciator. The boat position annunciator can be a visual display for the operator of the marine vessel. In certain embodiments of the present invention, the rotor of the motor is operatively attached to a threaded shaft which rotates in response to rotation of the rotor. The threaded shaft can be operatively connected to the trim tab, whereby rotation of the rotor causes the threaded shaft to rotate and rotation of the threaded shaft causes the trim tab to move relative to the stator of the motor as it pivots about a pivot point attached to the transom of a marine vessel.
The signal output device can be a digital potentiometer which is configured to receive a digital signal which is representative of a change in the rotational position of the rotor relative to a preselected position, such as a preselected position that is associated with a horizontal position of the trim tab. The digital potentiometer provides a DC voltage signal which is representative of the stored digital count which, in turn, is representative of the cumulative change in the position of the rotor relative to the preselected position of the rotor relative to the stator. The direction determining circuit of the present invention can comprise a dual optocoupler. The present invention, in certain embodiments, can comprise a pulse conditioning circuit that is connected in signal communication between the counter and the signal output device in order to receive pulses from the counter and, prior to passing those pulses to the signal output device, the pulse conditioning circuit affects the timing and/or size of the pulses. In addition, the pulse conditioning circuit can be used to add pulses to the cumulative count as a function of whether or not the trim tab is being moved against the flow of water or with the flow of water.
Certain applications of the present invention provide a trim tab position monitor comprising a motor which has a stator and a rotor. The rotor is operatively connected to the trim tab to move the trim tab relative to the stator of the motor in response to rotation of the rotor of the motor relative to the stator. The sensing circuit is connected in electrical communication with the stator for sensing an electrical characteristic such as the voltage potential across the stator, of the motor. The sensing circuit comprises a signal conditioning circuit, a zero crossing detector, and a direction determining circuit. A counting circuit is configured to provide a series of digital pulses which are responsive to the signal conditioning circuit and to the zero crossing detector. A signal output circuit is connected in signal communication with the counting circuit and with the direction determining circuit and is configured to provide an analog output signal which is representative of a plurality of digital pulses and which is representative of the position of the trim tab relative to the stator. An output pulse conditioning circuit is connected between the counting circuit and the signal output circuit for controlling the timing and shape of the plurality of digital pulses. In a preferred embodiment, the motor is a DC motor and the signal conditioning circuit comprises a high pass filter, an amplifier, and a low pass filter. The direction determining circuit comprises a dual optocoupler and the signal output signal comprises a digital potentiometer. The stator of the motor, in a preferred embodiment of the present invention, is rotatably attached to a transom of a marine vessel and the rotor is attached to an actuator which is, in turn, attached to the trim tab.